A variety of industrial products are processed by immersion in hot and often corrosive liquids. Integrated circuit wafers, for example, are etched and cleaned in this manner. The chemical bath in which such articles are processed typically has a liquid receptacle formed of refractory material which seats in a casing formed of different material such as plastic. The receptacle is supported by an integral flange which overlays the casing rim. Mastic sealing material between the flange and the casing rim assures that internal components within the casing, such as thermal insulation, heating elements and thermocouples, will not be damaged by dripping chemicals, corrosive fumes or moisture.
Chemical bath seals of this kind tend to have an undesirably brief effective life. Among other causes, the materials of which such seals are formed are susceptible to chemical attack by liquids of the types that may be contained in the bath. Various processing activities, such as the removing of treated articles from the bath, may cause dripping of such liquids onto the exterior surfaces of the bath. Degrading of the seal is not limited to instances where the liquid comes into direct contact with the sealing material as fumes emitted by such liquids can also corrode the material. Chemical damage to the sealing material is aggravated by the high temperatures which are present in the vicinity of the seal.
Seal life can also be limited by the thermal cycling which occurs at a chemical bath. The sealant typically bonds three different materials together, the quartz or the like of the chemical receptacle, the plastic of the casing and the sealant itself. These materials undergo different amounts of thermal expansion when heated. This creates repeated stresses which tend to break the bonding of the sealant with the other materials and to disintegrate the sealant itself.
The present invention is directed to overcoming one or more of the problems discussed above.